This invention relates to a blood pump which employs diaphragm reciprocation into and from a blood chamber to propel blood through an extracorporeal circuit. In the past roller pumps have been used predominantly to assist blood flow in blood purification treatments outside the body. Such roller pumps usually comprise a length of blood tubing arranged in a generally circular arc and propel blood forward in slowly repetitive pulses as the roller compresses the tubing during rotation. Such peristaltic type pumps are satisfactory but do not readily lend themselves to adaptation and use with improved one-piece integral hollow fiber artificial kidneys of the type shown in U.S. Pat. No. 4,231,871.
Those familiar with current hemodialysis clinical usage of artificial kidneys and apparatus for controlling extracorporeal blood circulation during blood purification treatments or the like have long been aware of the desirability of providing a reliable blood pump fabricated sufficiently inexpensively such that the pump could be integrated with an artificial kidney and discarded along with the kidney after use.
The blood pump of this invention fills this need and provides a blood pump particularly suited for incorporation as an integral element into a hollow fiber artificial kidney of the type shown in U.S. Pat. No. 4,231,871. The pump of this invention is a small, lightweight single blood chamber equipped with a flexible diaphragm and inlet and outlet low resistance valves which alternately connect the blood chamber with either an inlet or outlet blood conduit.
Broadly speaking, diaphragm pumps are old in the carburetor and fuel pump arts. Flexible diaphragms have been used in fuel pumps having two or more chambers for feeding fuel to carburetors and certain constructions have employed flapper valves integral with a flexible diaphragm for controlling the flow of gasoline to the carburetor. This type of pump employs changes in crankcase pressure as the source of power for actuating the diaphragm and relies on high speed revolutions of the engine, between about two thousand and nine thousand revolutions per minute, to actuate the diaphragm at the same rate. Apparatus of this type is shown in U.S. Pat. Nos. 2,769,838, 3,045,605 and 3,250,224. These constructions are multiple chamber devices having a flexible diaphragm equipped with integral flapper valves having wide, high-momentum and high resistance hinge regions that flap at high speeds as the gasoline is fed to the carburetor. Such devices are unsuitable for use with blood because blood would be destroyed by hemolysis if pumped through such a device.
A single chamber fuel pump using a flexible diaphram which employs flap valves that are restrained by a web finger which restrains the flap from separating substantially or freely from the plane of the diaphragm and causes the fluid to pass through a small annular passageway is shown in U.S. Pat. No. 2,980,032. This construction is also unsuitable for pumping blood due to hemolysis that would result from the sharp directional changes and tortuous path flow that would result from its use. This type of flow is to be contrasted with the smooth, substantially unidirectional flow that occurs through the freely openable, low inertia, unrestrained flapper valves in the diaphragm of the blood pump of this invention.
Another type of diaphragm pump for use in intravenous delivery of fluids is shown in U.S. Pat. Nos. 3,976,402 and 4,165,208. These pumps employ a flexible diaphragm as a germ barrier sheath for a piston which reciprocates into and from a liquid supply chamber to cause float or gravity controlled valves to allow liquid to pass from the supply chamber to a delivery chamber equipped with similar valves.
The above described devices represent the most pertinent prior art known to applicant. Prior to the present invention, applicant is unaware of any blood pump using a single chamber equipped with a flexible diaphragm having integral low inertia, freely openable and closable flapper valves of the type employed in the pump of this invention.